A STOKER FOR BURNING SOLID FUEL

Abstract: A stoker for burning solid fuel, comprising a grate (14) which is connected to a fan (21) for supply of combustion air, and feeding means (11, 12) for controlled feeding of fuel from a reservoir (15, 17) to the grate (14). The reservoir on one hand comprises a primary container (15) located at the feeding means (11, 12) containing a smaller volume of the fuel, and on the other a secondary container (17) which is connected to the primary container and is located at a distance from said primary container and having a main volume of the fuel. The primary container comprises detector means (20a) for controlling replenishment of fuel from the secondary container to the primary container. An air distribution chamber (20b) is located between the grate (14) and the primary container (15), which chamber is supplied with air via the fan (21) distributing air to the grate bowl (14) via a primary air pipe (22), and to the upper side of the grate via a secondary air outlet (23). An outer ring (26) is rotatably journalled upon the upper edge of the grate bowl, and is provided with gear segments to rotate the ring (26) in order to avoid accumulation of cinders at the opening of the grate.

Description: TITLE A stoker for burning solid fuel TECHNICAL FIELD The present invention concerns a stoker for burning solid fuel, comprising a grate which is connected to a fan for supply of combustion air, and feeding means for controlled feeding of fuel from a reservoir to the grate which reservoir on one hand comprises a primary container located at the feeding means containing a smaller volμme of the fuel, and on the other a secondary container which is connected to the primary container and is located at a distance from said primary container and having a main volume of the fuel, which primary container comprises detector means for controlling replenishment of fuel from the secondary container to the primary container, wherein an air distribution chamber is located between the grate and the primary container, which air distribution chamber is supplied with air via the fan and distributes the air to the grate bowl via a primary air pipe, and to the upper side of the grate via a secondary air outlet. BACKGROUND OF THE INVENTION Combustion of non-fossil solid fuel, like for example pellets, wood, and wood chips, is normally performed in a grate. The solid fuel is slowly gasified within the grate under limited supply of air. The received gas is then burned in a secondary step under ample supply of air. The process results in a minimum discharge of environmental polluting gas, in comparison with most other types of combustion. The residual product is a fine ash which contains matter having a pH-increasing effect and being in shortage within acidificated ground. The development of furnaces for this purpose has been directed to furnaces which can be operated automatically, approximately in the same user friendly way as the existing oil burner. This has resulted in that large resources have been gone in for designing the automatic infeed of the fuel, and corresponding automatic ou feed of ash. The problems to solve at the infeed side has first of all been to fulfil fire safety demands, so that is ensured that the fire in the grate can not spread itself to the fuel reservoir. For the above reasons, furnaces and burners for solid fuel have been designed as a complete furnace or as a dockable unit which can be docked to an existing furnace. TECHNICAL PROBLEM One object of the present invention is to provide a stoker for burning solid fuel which fulfils the above mentioned fire safety demands and which has so small mounting space requirements, that it can replace conventional oil burners on a common heating boiler. THE SOLUTION For this object, the stoker according to the invention is characterized in that an outer ring is rotatable joumalled upon the upper edge of the grate bowl, and is provided with gear segments to rotate the ring in order to avoid accumulation of cinders at the opening of the grate. DESCRIPTION OF THE DRAWINGS The invention will now be described here below with reference to a preferred embodiment, which is shown in the attached drawings, in which Fig. 1 is a side view schematically showing a stoker according to the invention, and Fig. 2 shows the stoker in Fig. 1 in a view from above. DESCRIPTION OF A PREFERRED EMBODIMENT The stoker according to the invention is adapted to be mounted directly into the furnace opening which is used for mounting an oil burner at a common one-family house heating furnace. For this object, the stoker is provided with a mounting plate 10 with screw holes for mounting screws. A thick pipe 11 is rigidly connected to the mounting plate 10 extending transversely through this plate. The pipe 11 forms a bearing for a feeding screw 12, which is driven intermittently with a very low speed by means of a stepping motor 13. The motor 13 drives the screw 12, so that its thread feeds in the direction towards the at the opposite end of the tube 11 located, bowl shaped grate 14. A primary reservoir.15 is placed with its bottom at an opening in the tube 11, in such a way that fuel, for example stick shaped pellets, can fall down into the tube 11 from the reservoir 15 and be fed in the direction towards the grate 14. The primary reservoir 15 is connected via a hose 16 (or a pipe) to a secondary reservoir 17, which is shown in reduced scale in Fig. 1 and is provided with a worm screw 18 which is operating obliquely upwards and is driven by a motor 19. The secondary reservoir 17 forms a main volume of fuel, which for example accommodates fuel for a month production of heat. The primary reservoir 15 forms a part volume which may be sufficient for about one hour production of heat. A level detector 20a in the primary reservoir 15 can for example be constituted by a photo cell, which is used for detection of the fuel level in this reservoir. At the detection of a sinking level below a certain level, a relay will switch on and start the motor 19 which will drive the screw 18, until a suitable level of fuel is reached inside the primary reservoir 15. Then the motor 19 is stopped. In this way it is ensured that only a limited amount of energy is present near to the fire in the grate 14. The tube 11 and the reservoir 15 are provided with temperature sensors (not shown in the drawings) which sense if anything unusual is would happen, wherein the motor 13 will increase its rate of feed and rapidly feed out the amount of fuel which is present in the reservoir 15, via the grate. Simultaneously, a signal is sent to the motor 19 so that its operation is stopped until the fault is corrected. An air distribution chamber 20b is located at the mounting plate 10 and is supplied with air via a fan 21. The chamber b is connected to the grate via a primary air pipe 22 and a secondary air pipe 23. The first mentioned pipe distributes air around the inside of the grate bowl 14 via slits 24 in a cast steel ring 25. The secondary air pipe 23 is directed towards to the upper edge of the grate bowl, above which the final combustion takes place. The secondary air also transports away the fine ash from the top of the grate bowl. An outer ring 26 is rotatable joumalled upon the upper edge of the grate bowl, and is provided with gear segments, which are actuated by a finger 28 protruding from the end of the screw shaft 12. Each time the finger 28 sweeps onto the gear segments of the outer ring, the ring 26 is turned a small amount forward. By this slow driven rotation of the ring 26, a levelling of the contents in the grate bowl 14, without concentration of said contents, so that accumulation of cinders at the opening of the grate can be avoided. A detection pipe 27 which extends from the air distribution chamber 20b through the mounting plate 10, is used for detection of the existence of combustion in the grate 14. The detector is cooled by means of leak air from the chamber 20b. Similar pipes can be used for detecting the level of ash in the furnace below the stoker, and for sucking out ash from said room. An electronic control system is used for indication of malfunction and for regulating the stoker with reference to feeding in of fuel via the screw 12. In this case, the stoker can be operated intermittently in the same manner as an oil burner, so that it can switch between a stand by mode (0 KW) and working mode (e.g. 2-12 KW), in accordance with thermostat control means. A stoker in accordance with the invention, can for example have an output of 2-12 KW. The combustion efficiency is about 90%. The amount of ash is normally 0,5-1 % and the weight of the stoker without secondary reservoir is about 10 Kg. The invention is not limited to the above described embodiment, but several variations are possible within the scope of the accompanying claims. For example, the grate 14 and the primary reservoir 15 can be designed differently.

Claims: CLAIMS 1. A stoker for burning solid fuel, comprising a grate (14) which is connected to a fan (21) for supply of combustion air, and feeding means (11, 12) for controlled feeding of fuel from a reservoir (15, 17) to the grate (14), which reservoir on one hand comprises a primary container (15) located at the feeding means (11, 12) containing a smaller volume of the fuel, and on the other a secondary container (17) which is connected to the primary container and is located at a distance from said primary container and having a main volume of the fuel, which primary container comprises detector means (20a) for controlling replenishment of fuel from the secondary container to the primary container, wherein an air distribution chamber (20b) is located between the grate (14) and the primary container (15), which air distribution chamber is supplied with air via the fan (21) and distributes the air to the grate bowl (14) via a primary air pipe (22), and to the upper side of the grate via a secondary air outlet (23), c h a r a c t e r i z e d in that an outer ring (26) is rotatable joumalled upon the upper edge of the grate bowl, and is provided with gear segments to rotate the ring (26) in order to avoid accumulation of cinders at the opening of the grate. 2. A stoker according to claim 1, c h a r a c t e r i z e d in that the primary air pipe (22) is connected to the grate (14) via slits (24) which are distributed around the inside of the grate bowl. 3. A stoker according to claim 1, c h a r a c t e r i z e d in that the feeding means (11, 12) for feeding fuel to the grate (14) are constituted by a screw conveyor. 4. A stoker according to claim 3, c h a r a c t e r i z e d in that the screw conveyor (11, 12) is connected to the primary chamber (15) at its bottom, extending horizontally between a drive motor ( 13) and an upwards turned, bowl shaped grate (14). 5. A stoker according to claim 1, c h a r a c t e r i z e d in that the fan (21) is located between the air distribution chamber (20b) and the primary reservoir (15), principally in parallel with the screw conveyor ( 11, 12) . 6. A stoker according to claim 1, c h a r a c t e r i z e d in that the primary reservoir (15) is provided with a level detector (20a) which controls the feeding of fuel from the secondary reservoir (17). 7. A stoker according to claim 6, c h a r a c t e r i z e d in that the secondary reservoir (17) is equipped with a worm screw (18), which is adapted to work obliquely upwards, in a direction towards an outlet which is connected to the primary reservoir (15) via a downwards directed chute (16). 8. A stoker according to any of the above claims, c h a r a c t e r i z e d in that the ring (26) is driven around intermittently by a finger (28) which is mounted at the end of the screw conveyor (11, 12).

Inventors: DANIELSSON BJOERN, DANIELSSON, BJOERN
Applicants: DANIELSSON BJOERN, E K TEKNIK PELLETSSYSTEM AB, DANIELSSON, BJOERN, E.K. TEKNIK PELLETSSYSTEM AB
Application year: 1994
Main classification: F23B1
IPC codes: F23K3